The present invention relates to a radiation image erase unit for erasing a remaining radiation image from a stimulable phosphor sheet by exposing the stimulable phosphor sheet to erasure light after light representing a stored radiation image has been emitted from the stimulable phosphor sheet by applying stimulating light thereto, and more particularly to such a radiation image erase unit capable of sufficiently erasing a remaining radiation image even when the erasure light is varied such as upon failure of erase light sources.
There has in recent years been proposed a radiation image recording and reproducing system in which a radiation image of an object can be produced by using a stimulable phosphor. The stimulable phosphor is a phosphor which, when exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, stores a part of the energy of the radiation. When the stimulable phosphor exposed to the radiation is subsequently exposed to stimulating light such as visible light, the stimulable phosphor emits light in proportion to the stored energy of the radiation.
The radiation image recording and reproducing system employs such a stimulable phosphor. More specifically, the radiation image of an object such as a human body is stored in a sheet having a layer of stimulable phosphor (hereinafter referred to as a "stimulable phosphor sheet"), and then the stimulable phosphor sheet is scanned with stimulating light such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected and converted to an electric image signal which is processed to reproduce a visible image on a recording medium such as a photographic film material or on a display unit such as a cathode-ray tube (CRT).
The aforesaid radiation image recording and reproducing system is disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, 4,387,428, and Japanese Laid-Open Patent Publication. No. 56-11395, for example.
The radiation image recording and reproducing system of the type described above is of greater practical advantage than conventional radiographic systems using a combination of an intensifying screen and an X-ray film in that images can be recorded in a wide range of radiation exposure. More specifically, it is known that the amount of light emitted from a stimulable phosphor upon stimulation thereof is proportional in a highly wide range to the amount of radiation to which the stimulable phosphor has been exposed. Therefore, even if the amount of radiation to which the stimulable phosphor is exposed varies widely under various conditions, radiation images free from such exposure variations can be obtained by selecting a suitable read-out gain in the photoelectric conversion means for detecting and converting the emitted light into an electric signal, and processing the electric signal into a visible image on a recording medium such as photosensitive material or on a display unit such as a CRT.
The radiation image recording and reproducing system is capable of processing a converted electric signal to produce a visible image on a recording medium or a display unit so that the radiation image can well be observed for diagnostic purpose. In this system, the stimulable phosphor sheet does not serve as a final image recording medium, but as a temporary image storage medium for eventually transferring images to the final recording medium or display unit. Therefore, the stimulable phosphor sheet can be used repeatedly or recyclically, and is economical and convenient if in repetitive use.
To reuse the stimulable phosphor sheet, the remaining radiation energy on the stimulable phosphor sheet after the radiation image has been read out by stimulating light is discharged by exposure to light, and the stimulable phosphor sheet is employed again for recording a radiation image thereon. The erasure of the radiation energy from the stimulable phosphor sheet is disclosed in U.S. Pat. No. 4,400,619, for example.
An image erase mechanism for removing the remaining radiation image from the stimulable phosphor sheet has erase light sources capable of emitting erasure light of as great illuminance as possible in order to cause almost all remaining radiation energy to be emitted from the stimulable phosphor sheet.
The erase light sources generally comprise a plurality of discharge lamps that are normally kept energized in an erase unit, i.e., in its casing. Therefore, while they are in use for a long period of time, the illuminance of light emitted therefrom is lowered or the discharge lamps fail to emit light because of their limited service life or the like. When this happens, the remaining image on the stimulable phosphor sheet cannot be erased completely, and the stimulable phosphor sheet cannot be used recyclically. If the stimulable phosphor sheet with a remaining image thereon is used again, a new object image will be recorded on the stimulable phosphor sheet in overlapping relation to the remaining image, and hence no accurate object image can be reproduced from the stimulable phosphor sheet. Since the erase light sources are housed in the erase unit, and the erase unit and an image read-out mechanism are mounted in an apparatus housing, it is impossible to check the erase light sources for their proper energization from the exterior of the housing.